The formulas
Sale price = Original × (1 − Discount%)
Discount% = (Original − Sale) ÷ Original × 100
Common discount percentages
| Discount | You pay |
|---|---|
| 10% off | 90% of original |
| 20% off | 80% of original |
| 25% off | 75% of original |
| 30% off | 70% of original |
| 50% off | Half price |
| 70% off | 30% of original |
| BOGO (buy 1 get 1) | 50% off pair |
FAQ
How do stacked discounts work?
They multiply. A 20% off sale with an extra 10% coupon = 0.80 × 0.90 = 0.72 of original, i.e. 28% off, NOT 30% off.
Is tax applied before or after discount?
Usually after — tax is on the discounted price, so you save on the tax as well.